A Rottweiler that killed a woman's Jack Russell in a Melbourne park was not added to the dangerous dogs list because a council investigation found the smaller dog had "assaulted" the Rottweiler by barking at it.

Sarah James' beloved dog Jack died on December 29 last year after it was attacked while being walked by her mother Lorna Harris in a Wattle Glen park, the Herald Sun reports.

Ms James said her 12-year-old dog never had a chance.

"The size and strength of the Rottweiler pulled her head clean through her collar," Ms James said.

Jack was rushed to a vet but could not be saved.

Ms James reported the attack to Nillumbik Shire Council and asked that the Rottweiler be put on a dangerous dogs list.

One year on that has still not happened, leading Ms James to accuse the council of bias because one of the rangers who investigated the incident told her that he had a Rottweiler and described smaller dogs as "nasty and aggressive".

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In a letter to Ms James the council said they did not have sufficient evidence to prosecute the Rottweiler's owner and an internal investigation had cleared the ranger of any wrongdoing.

Unprepared to let the matter go, Ms James took her complaint to the Ombudsman, who found the council's investigation was flawed, citing concerns about the ranger's interviews and poor record-keeping.

In response to the Ombudsman's probe Nillumbik Shire Council's regulatory services manager, Phil Lovelace, said their evidence showed the Jack Russell had started the fight by growling at the Rottweiler.

He said that this could be considered assault under the Domestic Animals Act.

Nillumbik Council chief executive Stuart Burdack said looking into the matter further would be "an irresponsible use of ratepayers' funds".